Checking Fuel Pressure On A 350 Tbi: A Step-By-Step Guide

To check the fuel pressure on a 350 TBI, you will need a fuel pressure tester. There are several options available on the market, including the Actron kit and the OTC 7665 fuel pressure adapter. The Actron kit is more affordable at $38, while the OTC adapter costs $53.95. Both options will require additional tools, such as wrenches, and it is important to exercise caution when working with gasoline. Once you have the necessary equipment, you can follow the instructions provided by the manufacturer to safely check the fuel pressure on your 350 TBI. It is important to note that acceptable fuel pressure readings for a 350 TBI are between 9 and 13 PSI, according to General Motors.

Check the fuel pressure regulator

Checking the fuel pressure regulator on a 350 TBI engine can help diagnose fuel pressure issues. The regulator is located inside the throttle body intake (TBI) unit. To check the fuel pressure regulator, you can perform the following steps:

• Identify the Fuel Pressure Specification: The stock fuel pump for a 350 TBI engine should provide a fuel pressure between 9 and 13 PSI, or 11 to 14 PSI according to some sources. It's important to know the correct pressure range before testing.
• Measure Fuel Pressure: Connect a fuel pressure gauge to the TBI unit. There are various methods to do this, including using an adapter at the TBI or fuel filter, or breaking the connection between the hard line and the flexible line to insert a tee fitting. Ensure you follow safety precautions as gasoline is highly flammable.
• Compare Measured Pressure to Specification: If the measured fuel pressure is within the specified range, the regulator is likely functioning correctly. If the pressure is lower than specified, there may be an issue with the fuel pump, a clogged filter, or a problem with the regulator itself.
• Further Testing of the Regulator: To specifically test the regulator, you can restrict the flow in the return line momentarily while running the pump. Be careful not to damage the return line. If the low-pressure reading surges well above the specified pressure, then the regulator is likely at fault.
• Consider an Adjustable Regulator: If you have made modifications to your engine, you may benefit from an adjustable fuel pressure regulator. This allows you to fine-tune the fuel pressure to match the requirements of your engine setup.

If you suspect issues with your fuel pressure regulator, it is recommended to consult a professional mechanic for further diagnosis and repair.

Check the fuel pump relay

To check the fuel pump relay, you will need to perform the following steps:

Firstly, locate the fuel pump relay. It is usually found in the engine compartment, often in a relay box or with other relays. The fuel pump relay may be labelled, or you can refer to your vehicle's service manual to identify it correctly. Once you have located the fuel pump relay, you can proceed to the next step.

The next step is to check the voltage at the fuel pump connection. To do this, you will need a multimeter or a voltage tester. Set your multimeter to measure voltage in the DC range, and connect the positive lead to the fuel pump connector and the negative lead to a good ground point. With the ignition key turned to the "on" position, but not cranking the engine, you should measure the voltage at the fuel pump connector. A typical voltage range for a 12-volt system is between 11 and 14 volts. If you measure voltage within this range, the fuel pump relay is likely functioning correctly. If you do not measure voltage within this range, there may be an issue with the fuel pump relay or another component in the circuit.

If you suspect an issue with the fuel pump relay, you can try swapping it with another identical relay, such as the horn relay, to see if the problem follows the relay. If the issue persists, it may not be the relay. However, if the problem is resolved, the fuel pump relay may be faulty and require replacement.

Additionally, you can inspect the fuel pump relay for any signs of damage, corrosion, or melting. If the relay appears damaged, it should be replaced. A visual inspection can sometimes identify a faulty relay, but keep in mind that relays can also fail internally without any visible signs of damage.

It is important to note that the fuel pump relay is not the only component that can cause fuel pressure issues. Other potential causes include a faulty fuel pump, a clogged fuel filter, a faulty fuel pressure regulator, or electrical issues such as a blown fuse or a faulty wiring harness. Therefore, it is essential to perform a comprehensive diagnosis, including checking the fuel pump relay, to identify the root cause of the problem.

Check the oil pressure switch

To check the oil pressure switch on a 350 TBI, you'll need to locate the oil pressure switch and the oil pressure sending unit. The oil pressure switch is usually located under and behind the distributor against the firewall, while the sending unit is typically found under the engine, right above the oil filter.

Once you've located the oil pressure switch, you can start the inspection process. Begin by observing the condition of the switch and its wiring harness. Look for any signs of damage, corrosion, or loose connections. If you notice any issues, it may be necessary to replace the switch or repair the wiring.

The next step is to check the functionality of the oil pressure switch. This can be done by using a multimeter to test the continuity of the switch. With the ignition turned off, disconnect the electrical connector from the switch. Set your multimeter to the continuity testing mode and touch the probes to the appropriate terminals on the switch. The specific terminals to test may vary depending on the switch design, so refer to a repair manual or consult a mechanic if you're unsure. A functioning switch should show continuity between the appropriate terminals.

In addition to the oil pressure switch, you should also inspect the oil pressure sending unit. This component sends a signal to the oil pressure gauge, providing a reading of the engine's oil pressure. To test the sending unit, you can use an oil pressure gauge tester, which can be purchased from automotive stores or online. Connect the tester according to the instructions provided, taking care to avoid over-tightening the connections. Start the engine and observe the oil pressure reading on the tester. Compare this reading to the one indicated on the dashboard gauge. If there is a significant discrepancy or the reading is outside the normal range, the sending unit may need to be replaced.

It's important to note that checking the oil pressure switch and sending unit requires working near the engine and fuel system. Always exercise caution when performing these checks to avoid the risk of injury or damage. If you're uncomfortable with the procedure, it's recommended to seek assistance from a qualified mechanic.

Check the fuel pump voltage

To check the fuel pump voltage on a 350 TBI, you will need to use a voltmeter. Here is a step-by-step guide:

• Locate the fuel pump: The fuel pump on a 350 TBI is usually located inside the fuel tank. You may need to refer to a repair manual or seek assistance from a mechanic to locate the exact position.
• Access the fuel pump: Depending on your vehicle's configuration, you may need to remove the back seat, a panel in the trunk, or the fuel tank itself to access the fuel pump. Again, refer to a repair manual or seek professional help if needed.
• Identify the wiring: Once you have located and accessed the fuel pump, you will see that it is connected to the vehicle's electrical system by a wiring harness.
• Set up the voltmeter: Connect the voltmeter to the wiring harness of the fuel pump. Ensure that you are measuring the voltage between the positive and negative terminals of the fuel pump.
• Measure the voltage: With the voltmeter connected, turn the ignition key to the "On" position but do not start the engine. You should now be able to read the voltage on the voltmeter display. A typical fuel pump voltage reading should be around 12 volts.
• Interpret the results: If the voltage reading is significantly lower than 12 volts, there may be an issue with the electrical system or the fuel pump itself. If the voltage reading is within the normal range, the fuel pump is likely functioning correctly.

It is important to note that working on fuel systems can be dangerous due to the presence of flammable fuels and high pressures. Always take appropriate safety precautions and consider seeking professional assistance if you are unsure about any part of the process.

Check the fuel supply lines

To check the fuel supply lines, you will need to remove the air cleaner and locate the throttle body. You will then need to take off the throttle body's fuel line nut that is closest to you, as well as the actual fuel line, using a 3/4" open-end wrench and a 3/8" or 7/16" line wrench.

Next, take the fuel line adapter and screw it into the throttle body. Be careful not to over-tighten, as the adapter is made of brass and will easily strip inside the steel threads. Connect your fuel line, again being careful not to over-tighten. Connect your fuel gauge before you start the truck. This fitting is what was used on old R12 air conditioning systems, and leaks quite a bit while connecting the gauge. Leaking gasoline on top of your engine can be dangerous. It is recommended that you tuck the gauge under the hood and hold it by your door while you stand outside the truck and crank it. That way, you can watch the truck prime, and how the pressure looks after it's running.

Acceptable readings, as per what General Motors says, is between 9 and 13 PSI. A little higher than 13 PSI won't hurt, but anything lower than 9 will definitely impact performance. Turn off the truck before disconnecting the fuel pressure gauge.

Another method involves using a generic OTC brand fuel filter adapter. For this, you will need a fuel pressure gauge, penetrating oil, a line wrench, and possibly an assortment of other wrenches to hold the fuel filter. It is also recommended that you buy a new fuel filter, as you will have your old one off already. Have buckets and lots of rags or paper towels handy, as your fuel lines will be gushing fuel while you fiddle with the filter. The filter is located on your frame rail, just underneath where the driver seat is. You will want to hold the fuel filter while you try to loosen the line nuts with your line wrenches. Do not use any other kind of wrench on these nuts! Take your time, as your fuel filter may be rusty. Your goal is to remove the fuel filter and install the adapter in its place. So, if you break your fuel line trying to get the filter out, it will need to be repaired before you can test your fuel pressure.

The Actron tester is preferred by some, as it comes with a gauge that makes reading low pressure easy, it also makes cleaning your injectors easy with a professional cleaning machine, and you don't have to lay under the truck to mess with the fuel lines and filter.

Frequently asked questions